This invention relates generally to clothes washing machines of the vertical axis, center-post agitator type, and more particularly to an automatic self-cleaning lint filter arrangement for separating the lint during the washing action to prevent redeposition on the clothes.
Automatic clothes washing machines of this type have a stationary outer tub mounted in a cabinet and accessible through a door on the top surface. Mounted within the stationary tub is a spin tub or basket within which is mounted on the central vertical axis an agitator having radially extending vanes. During washing or rinsing action, the spin tub is generally held stationary or prevented from rotating in its normal direction while the agitator is oscillated back and forth to provide the necessary washing action. To extract the water from the clothes so that they may be further dried, the spin tub is rotated at the high rate of speed so that centrifugal force forces the water outward through perforations in the side wall of the spin tub in the outer tub from which it is pumped to drain. Generally the washing machine has a transmission driven by a bidirectional electric motor which functions so that when the motor is rotated in one direction the transmission drives the agitator in its reciprocating motion, and when the motor is reversed, the transmission drives the spin tub and agitator as a unit to provide the water extraction action. The water can be drained during the spin cycle by a pump driven directly by the motor, and which functions to pump water out of the tub only when it is rotating in the spin direction.
One particular problem with the washing action of such automatic clothes washer is that of lint, which may occur on the surface of the clothes to be washed and may be produced to some degree by the washing action. Unless the lint is separated, it remains mixed with the clothes and will be redeposited on them during the spin operation. Accordingly, several methods have been proposed to provide a filtering action to separate the lint during the washing cycle so that the lint can be separated from the wash water for later disposition.
One method of providing a lint filter is to take advantage of the fact that the pump may be driven in both directions by the bidirectional motor that functions only during the spin cycle to withdraw water from the outer tub. The pump may be provided with a secondary pumping mechanism in a second chamber which functions when the motor is rotating in the opposite direction during the wash cycle, and thus pumps water from the drain at a very low rate and recirculates it back to the tub after passing through an external lint filter which may be removed from the machine and cleaned at the end of a complete clothes washing cycle. Such filters depend upon the efficiency of a recirculating pump, which has disadvantages in that it may produce excessive aeration and problems with high sudsing detergents, as well as requiring a separate cleaning action which, if forgotten by the user, may result in the filter's becoming completely clogged and ineffective.
One arrangement which avoids the use of a recirculating pump is to use the flow of water around and through the agitator, as shown in T. R. Smith U.S. Pat. No. 2,976,711. By providing an internal flow within the agitator, a separable lint filter can be mounted in the center and is easily removed for cleaning at the end of a wash cycle.
The arrangement described above still requires removal and cleaning of a lint filter, and various efforts have been proposed to provide a lint filter which has a self-cleaning action so that the user does not have to remember to perform the filter cleaning operation at the end of each wash cycle.
One approach has been to provide a filter in the bottom surface of the spin tub close to the central bearing hub, and is shown in the U.S. Pat. No. 3,352,130 of W. G. Landwier and E. B. Ruble U.S. Pat. No. 3,910,076. In these washing machines a plurality of openings are spaced around the bottom wall of the basket and mount screen-type filter elements having a suitable size perforation to allow water to float freely therethrough but cause the lint to collect on the bottom surface. With this arrangement, the agitator has a plurality of radial vanes on the undersurface adjacent the bottom wall of the spin tub radially outward from the lint filter openings. As the agitator oscillates back and forth, these vanes provide a pumping action, causing water in the outer tub to be pumped upwardly through the individual filters to the interior of the spin tub, from which it can recirculate back to the outer tub through the various openings. When the spin tub goes into a high rate of spin, the centrifugal force will cause the water to flow radially outwardly across the bottom surface of the lint filters so that the lint is then drawn off with the drain water through the pump. However, such arrangements tend to make it rather costly to manufacture the individual filter elements, and the presence of the large number of large openings in the bottom wall of the spin tub at this point may cause a serious structural weakness and possible flexing and failure of the material of the spin tub.
Another approach to overcome the above problems is shown in patents of R. B. Sherer et al. U.S. Pat. No. 4,357,813 and S. L. McMillan et al. U.S. Pat. No. 4,455,844. These arrangements allow the use of much smaller holes in the bottom wall of the tub and use the vanes on the underside of the agitator for a pumping action. However, the filter itself is maintained on a separate plastic filter element attached to the underside of the spin tub and providing the necessary filter screen and flow passages so that the water flows upwardly through the filter, radially inwardly along the passages, upwardly through smaller openings in the bottom wall of the spin tub near the hub, and then back into the interior through the pumping action of the agitator vanes.
All of the foregoing prior art arrangements have been employed with spin tubs made from metal, such as steel, and generally protected by porcelain enamel. Recently, it has been proposed to utilize spin tubs that are formed from a suitable plastic material such as a filled polypropylene in which the tubs can be manufactured by injection-molding and require little additional finishing or preparation. Such plastic spin tubs can result in a reduced manufacturing cost, as well as improved performance, by being free of rust without further treatment. However, this requires that the design of the spin tub be reconsidered because of the change of materials, and thus none of the prior art solutions to the selfcleaning lint filter problem have proved satisfactory with a plastic spin tub.